This invention relates to a process for the preparation of siloxane-oxyalkylene copolymers by the hydrosilylation reaction of an organohydrogensiloxane and an olefinically substituted polyoxyalkylene in a monocarboxylate ester of an alkanediol solvent In one aspect, this invention is directed to a process for the preparation of improved siloxane-oxyalkylene copolymer compositions. In a further aspect, the invention is directed to siloxane-oxyalkylene copolymers that are suitable for use as surfactants in urethane foam applications.
The hydrosilylation reaction between the organohydrogenopolysiloxane and an olefinically substituted polyoxyalkylene reactant is typically performed in a low molecular weight volatile hydrocarbon solvent such as benzene, toluene, xylene or isopropanol so as to promote the solubility of the reactants, to aid in handling the reactants or to moderate an exothermic reaction. Less typically, the hydrosilylation reaction may be conducted without a solvent such as disclosed in U.S. Pat. No. 3,980,688 or conducted in an oxygen containing solvent such as an ether, a polyether, or a lower or higher molecular weight alcohol.
For example, U.S. Pat. Nos. 3,280,160 and 3,401,192 disclose the preparation of copolymers in n-butylether and in a 50/50 mixture of isopropyl alcohol/toluene, respectively. In U.S. Pat. No. 4,122,029 the use of isopropyl alcohol is disclosed and in U.S. Pat. No. 3,518,288 the patentee teaches the use of n-propanol/toluene as a suitable solvent for the preparation of siloxane-oxyalkylene copolymers. The particular solvents employed in U.S. Pat. No. 4,857,583 are saturated polyols containing two or more hydroxyl groups U.S. Pat. No. 4,857,583 states that if one were to use copolymers containing monohydric higher alcohols in urethane foam applications, these alcohols will enter into the urethane reaction and act as reaction chain terminators in a detrimental fashion because they contain only one hydroxyl group.
Of the above mentioned solvents, isopropyl alcohol (IPA) is the most common solvent used. IPA is known to compatibilize the siloxane and the glycol(s) so that the reaction proceeds more readily. However, disadvantages to using IPA exist. Such disadvantages include: (1) IPA competes with the vinylated glycol for SiH sites on the siloxane backbone resulting in the formation of isopropoxy which acts as a defoamer and contributes to surfactant instability; (2) IPA reacts with isocyanate effectively lowering the index of the formulation, therefore, the IPA must be stripped from the product and recovered, a process which is both time consuming and expensive; (3) IPA is miscible with water which is harmful in the manufacture of polyurethane foam surfactants; and (4) IPA is flammable which creates additional manufacturing problems. In addition, surfactants manufactured utilizing IPA cannot be restripped without destroying the performance of the surfactant.
In contrast to the teachings of the prior art, the present invention utilizes a monocarboxylate ester of an alkanediol solvent which contains only one hydroxy group. Such a solvent, however, does not have the disadvantages associated with it as are present when using IPA. The present inventors have discovered that such monocarboxylate ester solvents react only minimally with SiH on the siloxane backbone. The monocarboxylate ester solvents also do not need to be stripped from the product and recovered. In addition, the monocarboxylate ester solvents are not hygroscopic and therefore the problems associated with water contamination are alleviated. Furthermore, the monocarboxylate ester solvents are not flammable.
It is therefore an object of the present invention to provide an improved process for the preparation of siloxane-oxyalkylene copolymers. Another object of this invention is to provide a process for the preparation of siloxane-oxyalkylene copolymers which are useful in the formulation of urethane foams and which contain a monocarboxylate ester of an alkanediol solvent. These and other objects will readily become apparent to those skilled in the art in the light of the teachings contained herein.